I have always been curious about this, but never thought to ask until now.
On my '90 S4 the temp gauge red line (overheat) is at 210*. Lately, the needle sits on the white line that's between 170* and 210* which according to my calculation is 190*.
My question is why is the overheat temp 210* ? On my previous car ('98 TransAm- also an aluminum block and heads V8) and many other cars, the overheat temp is at 260* on the gauge.
Does the 928 measure the temp from somewhere different than other cars? Why such a low overheat temp? It's not an issue because even in Phoenix where the temp today was 109* cruising at 75mph on the freeway and front and rear air on, it didn't get past that last white temp gauge line.
Just curious.
Jay in Az

 

Hi Jay,

Thanks for posting this question. I have the same issue with my 1990 S4. The only difference is with mine is that the needle sometimes gets above the last white line, almost half way between the last white line and the start of the red, overheat zone. This only happens when it's over 100 F outside. I've had this checked out by Devek who says that this is normal.

In the couple of years I've had my 928, I've noticed that all the gauges are much more "active" than they are in any other car I've driven. In every other car I've driven the temp gauge goes right to the middle and stays there, no matter what is happening outside. On the 928, I can see the temperature gauge move with changes in the outside temperature. When going up grades and back down grades I can see the gauge move up as I climb the grade and then way back down again as I descend the grade. I actually like seeing the changes as the engine is exposed to differences in outside temperature and load but I've always wondered if this is OK.

Jim

 

Actually, the upper white line is 210 degrees F. The redline above it is about 240 degrees F.

This information is in the Owner's Manual.

 

Jim & Jay -

This is normal for the '89 and above cars with the "improved" gauge cluster. My '90 GT and previous '89 S4 would run right around the white 210 degree mark most of the time. In cool weather a needle two short of the line, in hot weather with A/C on....right on the line or slightly over.

Bought a laser temp gun and took several readings on it for several months, seasons, etc.
If anything, the temp gauge in the cluster was reading slightly higher then the engine was running.

Seat of the pants observation is that the later model cars like to run a little hotter.....indeed my GT runs the BEST when the temp needle is around the white line. Anything before that and it feels a little sluggish.

Now why did Porsche decide to put a temp gauge in the car that was "normal" at the 3/4 mark??, when it has been burned into us Americans that the needle being at 1/3 or 1/2 mark on the temp gauge has always been normal....who knows.

 

It seems that Porsche designed all the gauges with a small enough range that you can see the normal changes in the engine's operation. The oil pressure gauge goes to 5 bar whenever you are moving but swings all the way down to 2 or 3 bar at idle. The temperature gauge like we observed also moves as loads and outside temperatures change. At first all these alarmed me but now it's kinda cool to see readings change as conditions change. It seems that gauges were designed to actually communicate to the driver what's happening under the hood. It's much more fun and interesting than those gauges in other cars that go right to the middle and stay there. It's almost like the beast is alive under there ;-)

 

I agree with everything Mike said. My 83 runs pretty much normal thru out the year. In Phoenix the sharks change around 10:45 am the heat kicks in and sharks heat up much faster.

With the AC on full, my shark will run around the top white needle or just above while sitting in traffic. Then it goes back down if you get a 1 mile run to the next light or freeway driving.

Turning the AC off and you seem to lift a load off the sharks back heat wise. I noticed the shark seems more oiled up when its at the 210 mark.

I saw a yellow Ferrari 355 in Chandler yesterday. I wasn't in my shark or I'd be temped to try and keep up with this monster if you know what I mean. My girlfriend refused to pace it in her Honda. It shot away and the engine sounded like music to me.

 

Interesting stuff. That gauge is deceptive- the 210 is much closer to the red area than it is to the third white line. The owners manual doesn't specifically say what temp the red line on the gauge is either. The only thing I found out is that the overheat warning light will come on at 250*.
It's good to know that my car is acting normal.
And Jim, you are right, the gauges on my car too move more than any other car I've owned. Not so much the temp gauge- it kinds of stays pretty much even when it's as hot as it is here, but the oil pressure is always moving from 20 to 50, when going from idle to cruising speed. And same with the volts gauge. Mine goes from about 13 (mid gauge) down to about 11 sometimes. The manual says it should generally stay between 12 and 14, but may go lower and if it goes too low the warning light will come on- mine hasn't so I guess that's not an issue either.
This list is invaluable. I am happy my car is normal.
Take care and thanks for the responses.
Jay in Az

 

IT MAY BE NORMAL BUT, WHEN I SEE THE NEEDLE CREEP UP TO THE THIRD WHITE LINE, I FEEL AS IF THE CAR IS SUFFERING. IT'S A BIT UNEASY CONSTANTLY WATCHING YOUR TEMP GAUGE. TODAY I TOOK MY DODGE TRUCK OUT TO NY IN 95 DEGREE HEAT WITH THE A/C ON FULL BLAST AND THE NEEDLE NEVER PASTED THE MIDDLE. IT GIVES ME PEACE OF MIND. NOT THAT I DON'T ENJOY DRIVING MY CAR, BUT BEFORE I DO I CHECK THE WEATHER, WIND, HUMIDITY, JUST JOKING, BUT I DO CHECK TO SEE IF IT GOES OVER 85 DEGREES THEN I JUST TAKE THE TRUCK. RENO

 

Reno, please do not type in all caps. It is hard to read, and realy annoying. Thank you.

I did notice something. On my family's Fords, the bottem of the volt meter is at 8 volts, and the top is at 18 volts. On my 928, the bottem is at 10, and the top is at 16. Thats a sigificantly smaller range, and voltage changes will result in a much greater swing.

I also noticed that my temp guage moves alought too. When in in stop and go traffic, in hot weather, with the a/c on full blast, it come all the way to just over the top white line, and stays there. According to my owner's mannual "Under normal driving conditions, needle should remain in center field. The needle may reach the red feild, especially at high engine loads, but should return to "normal" when engine load is reduced." That makes me feel OK about it.

 

In all street driving conditions, I've never seen anything higher than 5/8 on my temp gauge at any time, including when running the AC compressor. I did notice a needle's- width increase on the gauge after replacing the instrument PCB foil. I have a great fan clutch, clean fins on the radiator and condenser and fresh coolant at a 45% mix with water wetter.

In hot summer autocross, I did hit 3/4 after a couple of very spirited runs, so I just added a manual override switch for the aux fan for constant on during autocross events. I haven't used it yet.

BTW, I'm confident about the gauge's accuracy because if the car was running hotter than what the gauge reads, the aux fan would cycle more frequently than it does.

Greg

 

Reno, etal:
I too was once a "temp gauge watcher worry wart". However, while doing DE events, I learned the 928 engine cooling system was far more robust than the gauge lead me to believe. Overheating does not occur till over 240 degrees F., and even then there is a 15+ degree cushion.

I realise the advice I'm about to give may be hard to follow, but it's time to change your temp gauge paradym. When the gauge gets to the upper white mark - consider that to be its most efficient temp. YMMV.

 

For a newbie (and of the "OLD" paradigm) I too was concerned about temp gauge at the upper white mark. Thanks to everyone now I am much at ease... however, I am installing the new 75° temp switch to turn on the aux fan earlier just to be safe.

 

"temp gauge watcher worry wart". LOL.

I think its quite common to keep your eye on that temp gauge if you live in AZ or any other place that gets over 100. Last year we had over 110 for like 45 days.

I hate to run the shark too much when its 110+. I now realize that I shouldn't freak out when the needle hits the high white mark. But I'll still keep my eye on it incase it goes to the red mark. Then its time to panic.

 

<----"temp gauge watcher worry wart".

I beleive you ED, with all the track time you have you should know.

I still will be seperating the trans and oil cooler from the radiator this summer

 

Hi,

Jay S - the cooling system in the 928 is indeed a difficult one to grasp as the 928's radiator is a heat "sink". In the past much has been written here about it - the following may help you too

The following extract is from a post here on the 30th April this year titled "Oil Condition Report No 2 "

Starts:

Yes, I have taken temperature readings and the averages follow;

Ambient - 26C M31-L23
Gauge - 85C M85-L87 Est
Thermo housing - 85C M88-L78
Top hose - 76C M88-L61
Bottom hose - 79C M90-L72
Valve covers - 88C M90-L85
Vee - 88C M90-L85
Oil cooler top line - 77C M88-L71
Oil cooler bottom line - 77C M90-L70
ATF line top - 63C M63-L52
AFT line bottom - 56C M54-L50

Ends

Note: the M is for maximum and the L is for Lowest and C is for Celsius

If you like, I can send you a document I prepared on this subject on our "Landshark" forum here in Australia.
Contact me direct via e-mail if you wish

I am still monitoring the temps. and can confirm the previous comments here from others that the temperature gauge is an "active" one. If the cooling system is in good condition, the engine's "core temperature" is very well managed within the system - and remarkably stable in a variety of conditions

Regards